Transparent Colloidal Crystals With Structural Colours

Spatially ordered arrangements of spherical colloids are known to exhibit structural colours. The intensity and brilliance these colours typically improve with colloidal monodispersity, low concentrations point line defects increasing refractive index contrast between the embedding medium. Here we show that suspensions charge stabilised, fluorinated latex particles refractive-index their aqueous background form Wigner crystals FCC symmetry for volume fractions 13 40%. In reflection they both strong, almost angle-independent sharp, more brilliant Bragg peaks despite particle polydispersity bimodal distribution. Simultaneously, appear transparent in transmission. Furthermore, binary AB, A 2 B type mixtures similarly sized polystyrene appeared predominantly white but clear indicating a CsCl-like BCC structure complex crystals. We characterised using combination reflectivity measurements small-angle x-ray scattering, complemented by modelling.